THE LIFE CYCLE OF FASCIOLOIDES MAGNA (BASSI, 1875), THE LARGE LIVER FLUKE OF RUMINANTS, IN CANADA: WITH OBSERVATIONS ON THE BIONOMICS OF THE LARVAL STAGES AND THE INTERMEDIATE HOSTS, PATHOLOGY OF FASCIOLOIDIASIS MAGNA, AND CONTROL MEASURES

Abstract

The life history of Fascioloides magna in Canada has been elucidated, the intermediate hosts being two fresh-water gastropods, Fossaria parva (Lea) and Stagnicola palustris nuttalliana (Lea). The morphology and bionomics of the egg and larval stages are described, particular attention being given to the nonparasitic stages. The ecology of the gastropod hosts in Canada is briefly described.A histopathological study of the lesion in definitive hosts reveals that this parasite in large Bovidae causes a severe tissue reaction. The lesion in these animals is generally in the form of a closed fibrous cyst from which eggs are unable to pass, and thus the life cycle cannot be completed. In Cervidae, the cavity in the liver is connected directly with the bile duct system, and there is a free egress of ova. From these facts it is inferred that this parasitic disease can only occur in the presence of Cervidae.Laboratory animals have been artificially infested with maritae, thus extending the host records of the trematode.A brief historical review, a summary of the present knowledge of distribution and definitive hosts affected, and a description of the control measures, are included.